Multipass tubular heat exchanger and associated pass partition plate, channel cover, and methods

ABSTRACT

A multipass tubular heat exchanger utilizing a pass partition plate and a tubesheet is described which is suitable for use with high differential pressure tubeside fluid without deformation or dislocation of the pass partition plate, thereby avoiding the problem of tubeside fluid bypassing. The pass partition plate has an edge fitting into a corresponding groove in the tubesheet. The edge and the corresponding groove each have a radius of curvature about an axis extending generally perpendicular to the tubesheet.

FIELD

The present disclosure relates generally to multipass tubular heatexchangers, more particularly to multipass tubular heat exchangershaving tubesheets and pass partition plates.

BACKGROUND

Multipass tubular heat exchangers which exchange heat from one fluid toanother without mixing the fluids are widely used in a variety of sizes,configurations and applications. Heat is exchanged by flowing a firstheat exchange fluid referred to as the tubeside fluid within a pluralityof tubes surrounded by a second heat exchange fluid. The tubeside fluidtraverses the length of the tubes multiple times. At one or both ends ofthe plurality of tubes is a cover enclosing a space in fluidcommunication with the tubes, which is commonly referred to by a varietyof terms such as a channel, bonnet, header box, or head, depending onthe particular type of heat exchanger and application. Between theenclosed space and the tubes is a planar tubesheet with holes forreceiving the ends of the tubes. In order to direct the tubeside fluidthrough the tubes in the desired multiple passes, a pass partition plateis typically provided within the enclosed space(s). Typically the plateis welded within the cover, and the cover with the plate is structurallysecured to the rest of the heat exchanger so that the plate is heldfirmly against the tubesheet. A gasket is typically included between theplate and the tubesheet, creating a seal so that tubeside fluid cannotbypass the tubes. In other words, fluid entering an inlet side of theenclosed space is directed through the tubes before flowing into anoutlet side of the enclosed space.

In operation, the fluid pressure on the inlet side exceeds the pressureon the outlet side. This differential pressure, also referred to as theinterpass pressure, exerts a force on the pass partition plate whichacts to push the partition plate in the direction of the lower pressureoutlet side. The interpass pressure generally increases over time asfouling or tube plugging occurs. On occasion this pressure is sufficientto cause the plate to deform and to break contact with the tubesheet.This can have several detrimental effects. For one, once contact betweenthe partition plate and the tube sheet is broken, the tubeside fluid ispermitted to bypass the tubes, thus decreasing the flow and the amountof heat exchange accomplished by the exchanger. Another potentialproblem when the plate breaks contact with the tubesheet is that theplate may scrape against the ends of the tubes, breaking the sealbetween the tubes and the tubesheet thus introducing opportunities formixing of the heat exchange fluids. These problems often require plantshutdowns for repairs, including reshaping or replacing the passpartition plate.

It would be desirable to have a multipass tubular heat exchanger whichwould reduce the likelihood of the aforementioned problems.

SUMMARY

One embodiment of the invention relates to a multipass tubular heatexchanger comprising:

a plurality of tubes configured to contain a tubeside fluid, theplurality of tubes having at least one set of terminal ends;

a planar tubesheet comprising apertures for receiving the ends of thetubes and a groove for receiving a pass partition plate, the groovehaving a length, a thickness, two endpoints and a midpoint;

a channel having a tubeside fluid inlet and a tubeside fluid outlet, thechannel positioned adjacent the tubesheet such that the channel andtubesheet together define an internal space in fluid communication withthe tubes; and

-   -   a nonplanar pass partition plate positioned in the internal        space configured to divide the internal space into an inlet        space in fluid communication with the tubeside fluid inlet and        an outlet space in fluid communication with the tubeside fluid        outlet, thereby to prevent direct fluid communication between        the tubeside fluid inlet and the tubeside fluid outlet and to        direct fluid flow through the tubes, wherein the pass partition        plate has a mating edge which fits into the groove of the        tubesheet;

wherein the groove of the tubesheet and the mating edge of the passpartition plate each have a radius of curvature about an axis extendinggenerally perpendicular to the tubesheet such that the midpoint of thegroove is a greater distance from a straight line passing through theendpoints of the groove than the thickness of the groove.

Another embodiment of the invention relates to a multipass tubular heatexchanger comprising:

a plurality of tubes configured to contain a tubeside fluid, theplurality of tubes having at least one set of terminal ends;

a planar tubesheet comprising a plurality of apertures for receiving theends of the tubes;

a channel having a tubeside fluid inlet and a tubeside fluid outlet, thechannel positioned adjacent the tubesheet such that the channel andtubesheet together define an internal space in fluid communication withthe tubes; and

a nonplanar pass partition plate positioned in the internal spaceconfigured to divide the internal space into an inlet space in fluidcommunication with the tubeside fluid inlet and an outlet space in fluidcommunication with the tubeside fluid outlet, thereby to prevent directfluid communication between the tubeside fluid inlet and the tubesidefluid outlet and to direct fluid flow through the tubes;

wherein the pass partition plate has an edge which is fixed to thetubesheet, the edge having a radius of curvature about an axis extendinggenerally perpendicular to the tubesheet.

Another embodiment of the invention relates to a matching pass partitionplate and tubesheet for use in a multipass tubular heat exchangercomprising:

a planar tubesheet comprising apertures for receiving ends of heatexchanger tubes and a groove for receiving a pass partition plate, thegroove having a length, a thickness, two endpoints and a midpoint;

a nonplanar pass partition plate having a mating edge which fits intothe groove of the tubesheet;

wherein the groove of the tubesheet and the mating edge of the passpartition plate each have a radius of curvature about an axis extendinggenerally perpendicular to the tubesheet such that the midpoint of thegroove is a greater distance from a straight line passing through theendpoints of the groove than the thickness of the groove.

Another embodiment of the invention relates to a channel cover for usein a multipass tubular heat exchanger comprising:

a semi-enclosed channel having a planar open end and configured todefine an internal space when the open end is positioned adjacent aplanar tubesheet; and

a nonplanar pass partition plate having peripheral edges fixed withinthe channel and a free edge in the plane of the open end wherein thefree edge has a radius of curvature about an axis extending generallyperpendicular to the plane of the open end.

Another embodiment of the invention relates to a method of retrofittinga multipass tubular heat exchanger having an existing tubesheet and anexisting pass partition plate, comprising:

removing the existing tubesheet and the existing pass partition plate;

installing a planar tubesheet comprising a plurality of apertures forreceiving ends of heat exchanger tubes and a groove for receiving a passpartition plate; and

a nonplanar pass partition plate having a mating edge which fits intothe groove of the tubesheet;

wherein the groove of the tubesheet and the mating edge of the passpartition plate each have a radius of curvature about an axis extendinggenerally perpendicular to the tubesheet.

Another embodiment of the invention relates to a method of exchangingheat between a tubeside fluid flowing through a plurality of tubes in amultipass tubular heat exchanger and a fluid surrounding the pluralityof tubes, comprising:

introducing a tubeside fluid into an internal space defined by a channeland a planar tubesheet having a plurality of apertures, the internalspace being in fluid communication with a plurality of tubes having aplurality of a tubeside fluid inlet ends aligned with a first portion ofthe plurality of apertures of the tubesheet and a plurality of tubesidefluid outlet ends aligned with a second portion of the plurality ofapertures of the tubesheet; and

flowing the tubeside fluid into the plurality of tubes through the firstportion of the plurality of apertures and through the plurality of tubesbetween the tubeside fluid inlet ends and the tubeside fluid outlet endssuch that the tubeside fluid exits through the second portion of theplurality of apertures into the internal space;

wherein the tubeside fluid exiting the tubes is separated from thetubeside fluid entering the tubes by a nonplanar pass partition platedividing the internal space having an edge in contact with the tubesheetwhich has a radius of curvature about an axis perpendicular to thetubesheet;

wherein no bypassing of tubeside fluid occurs around the pass partitionplate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a heat exchanger according to the priorart.

FIG. 2 is an end view of a tubesheet for use in a heat exchangeraccording to one embodiment of the invention.

FIG. 2A is a section view partially illustrating the tubesheet of FIG.2, as seen along line 2A-2A.

FIG. 3 is a perspective view of a combination of a matching passpartition plate and tubesheet according to one embodiment of theinvention.

FIG. 4A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 4B-4D are diagrammaticend views of tubesheets for use in heat exchangers according toalternative embodiments of the invention.

FIG. 5A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 5B-5D are diagrammaticend views of tubesheets for use in heat exchangers according toadditional alternative embodiments of the invention.

FIG. 6A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 6B-6D are diagrammaticend views of tubesheets for use in heat exchangers according toadditional alternative embodiments of the invention.

FIG. 7A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 7B-7D are diagrammaticend views of tubesheets for use in heat exchangers according toadditional alternative embodiments of the invention.

FIG. 8A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 8B-8D are diagrammaticend views of tubesheets for use in heat exchangers according toadditional alternative embodiments of the invention.

FIG. 9A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 9B-9D are diagrammaticend views of tubesheets for use in heat exchangers according toadditional alternative embodiments of the invention.

FIG. 10A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 10B-10D arediagrammatic end views of tubesheets for use in heat exchangersaccording to additional alternative embodiments of the invention.

FIG. 11A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 11B-11D arediagrammatic end views of tubesheets for use in heat exchangersaccording to additional alternative embodiments of the invention.

FIG. 12A is a diagrammatic end view of a tubesheet for use in heatexchangers according to the prior art, and FIGS. 12B-12D arediagrammatic end views of tubesheets for use in heat exchangersaccording to additional alternative embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a multipass tubular heat exchanger 10 according tothe prior art. The heat exchanger includes a plurality of tubes 4 forcontaining a heat exchange fluid referred to as a tubeside fluid. Theplurality of tubes 4 has at least one set of coplanar terminal ends. Thetubes of the heat exchanger can be U-shaped tubes, also referred to as Utubes, as illustrated in FIG. 1, having all terminal ends, i.e., boththe tubeside fluid inlet and outlet ends, in a single plane. A heatexchanger utilizing U tubes is referred to herein as a U tube heatexchanger. Alternatively, the tubes may be straight, having inlet endsand outlet ends at opposite ends of the tubes. A heat exchangerutilizing straight tubes is referred to herein as a straight tube heatexchanger. At one or both ends of the plurality of tubes is an internalspace in fluid communication with the tubes defined by a semi-enclosedcover and a tubesheet. The semi-enclosed cover is commonly referred toby a variety of terms such as channel, channel cover, bonnet, headerbox, head and floating head, depending on the particular type of heatexchanger and application. For the purposes of this disclosure, the term“channel” is used to refer to the semi-enclosed cover regardless of thespecific type of heat exchanger. A U tube heat exchanger has a channel 8at one end of the plurality of tubes, as shown in FIG. 1. The channelincludes a tubeside fluid inlet 8A and a tubeside fluid outlet 8B. Astraight tube heat exchanger has a channel at each end of the pluralityof tubes (not shown). Regardless of whether the heat exchanger utilizesU tubes or straight tubes, the ends of the tubes are received byapertures 5A in a planar tubesheet 5 located adjacent the channelbetween the channel and the plurality of tubes. The ends of the tubesare sealed to the tubesheet 5. The tubes may be supported by cross-flowbaffles 13.

In a tubular heat exchanger, heat is exchanged by flowing a tubesidefluid within tubes in a plurality of tubes surrounded by a second heatexchange fluid. In a multipass tubular heat exchanger, the tubesidefluid traverses the length of the tubes multiple times. In order todirect the tubeside fluid through the tubes in the desired multiplepasses and to prevent direct communication between the tubeside fluidinlet and the tubeside fluid outlet, it is common practice to include apass partition plate 1 within the channel(s). Typically peripheral edgesof the plate are welded within the channel, and the channel and plateare structurally secured to the shell 12 or other structure of the heatexchanger so that an edge of the plate is held firmly against thetubesheet. The pass partition plate has a mating edge 1A which fits intogroove 5B of the tubesheet 5. This groove is typically 3-8 mm deep.Alloy or carbon steel is typically used as the material for the channel,the pass partition plate and the tubesheet. The pass partition platedivides the internal space within the channel into at least an inletspace in fluid communication with the tubeside fluid inlet and outletspace in fluid communication with the tubeside fluid outlet.

According to one embodiment of the present invention, the groove of thetubesheet and the mating edge of the pass partition plate each have aradius of curvature. FIG. 2 illustrates a tubesheet 6 for use in a heatexchanger according to one embodiment of the invention. Apertures 6A areprovided for receiving the ends of heat exchanger tubes. At least onegroove 6B is provided for receiving the edge of the pass partitionplate. Unlike the prior art groove(s) which are in the form of straightlines, the groove according to the invention has a radius of curvature.Referring to FIG. 2, the distance 16 between the midpoint of groove 6Band an imaginary line 14 between the endpoints of groove 6B is greaterthan the thickness of groove 6B. Distance 16 may be greater than thelength of line 14 divided by 100, even greater than the length of line14 divided by 50. The desired amount of curvature and the direction ofthe curvature, i.e. in the direction of the tubeside fluid inlet or thedirection of the tubeside fluid outlet, will vary depending on theparticular mechanical design considerations and process designconsiderations for the intended application. Relevant designconsiderations may include the particular materials for use in the passpartition plate, channel and tubesheet, the particular heat exchangefluids being used, the use of pulsating fluid, operating temperature andpressure, and two-phase phenomena such as boiling and condensing. Asillustrated in FIG. 2, the radius of curvature of the both the grooveand pass partition plate is defined about an axis that extends generallyperpendicular to the tubesheet, i.e., the radius of curvature is definedby the profile of the groove and plate when viewed in a directionperpendicular to the plane of the tubesheet.

According to one embodiment of the invention, a matching tubesheet andpass partition plate are provided, collectively denoted by referencenumeral 20 in FIG. 3. Pass partition plate 2 has a radius of curvaturealong its mating edge 2A to correspond to the radius of curvature of thegroove 6B, therefore the pass partition plate is nonplanar. Thethickness of the pass partition plate will vary according to theparticular design considerations of the intended application. In somecases, the pass partition plate and the groove can be curved to beconvex when viewed from the direction of the tubeside fluid inlet, i.e.,so that a positive differential pressure tends to flatten the passpartition plate. In other cases, the pass partition plate and the groovecan be curved to be concave when viewed from the direction of thetubeside fluid inlet, i.e., so that a positive differential pressuretends to bend the pass partition plate to a greater curvature. While thepresent invention is not limited to any particular theory of operation,it is believed that a convexly or concavely curved pass partition platecan provide more stiffness compared to a flat pass partition plate ofotherwise similar dimensions. Advantageously, because the plate has aradius of curvature and is therefore able to withstand greaterdifferential pressure, a thinner plate may be possible than conventionalflat plates. Alternatively, for an equivalent thickness plate, greaterdifferential pressures can be tolerated during operation than usingconventional flat plates.

As shown in FIGS. 2 and 2A, a gasket 22 is typically positionedimmediately adjacent and between the channel and the tubesheet 6. Thegasket may include a rib portion which acts as a gasket between the passpartition plate 2 and the groove 6B of the tubesheet, also referred toas a pass partition gasket. The material used for the gasket and the ribcan be any suitable material for the application such as, but notlimited to, metal, paper board, composite material, elastomericmaterial, and the like.

Multipass tubular heat exchangers which exchange heat from one fluid toanother without mixing the fluids are widely used in a variety of sizes,configurations and applications. Heat exchangers utilizing the featuresof the embodiments disclosed herein are not limited in these regards andare likewise useful in a wide variety of sizes, configurations andapplications.

According to one embodiment, the heat exchanger is a shell and tube heatexchanger. FIG. 1 illustrates a typical shell and tube heat exchangerwherein the tubes are housed within a shell 12 for containing a shellfluid, the shell having a shell fluid inlet 12A and a shell fluid outlet12B. The tubesheet 6 is secured to one end of the shell 12.

According to an alternative embodiment, the heat exchanger is an aircooled heat exchanger which does not include a shell, in which heat isexchanged between the tube fluid within the tubes and air moving overthe tubes. Typically in an air cooled heat exchanger, the pass partitionplate is fixed within the channel cover and also fixed to the tubesheetrather than fitted into a groove as described above. The plate may befixed to the tubesheet via welding or may be otherwise formed integrallywith the tubesheet.

The heat exchanger may have a floating tubesheet and floating head, asare known to those of ordinary skill in the art.

FIGS. 4-12 illustrate nonlimiting examples of additional shapes (endview profiles) of pass partition plate which may be used to partitionthe channel, according to the prior art as well as to the presentinvention. In each of FIGS. 4-12, the “A” view illustrates the end viewprofile of the pass partition plate(s) known in the prior art. The “B”through “D” views illustrate nonlimiting examples of various end viewprofiles of pass partition plates according to the present invention, inwhich curvature has been introduced to the corresponding prior artprofile.

As can be seen from these figures, multiple pass partition plates andmultiple grooves may be present in a given tubesheet. Many passes oftubeside fluid through the multipass tubular heat exchanger are possibleaccording to the present disclosure.

According to one embodiment of the invention, a method is provided forexchanging heat between a tubeside fluid and a fluid surrounding theheat exchanger tubes. Tubeside fluid is introduced into the internalspace defined by the channel and planar tubesheet and flows through aportion of the apertures in the tubesheet and through the correspondingtubes. The tubeside fluid exits through a second portion of theapertures in the tubesheet back into the internal space. The tubesidefluid exiting the tubes is separated from the tubeside fluid enteringthe tubes by the nonplanar pass partition plate dividing the internalspace having an edge in contact with the tubesheet which has a radius ofcurvature about an axis perpendicular to the tubesheet. Advantageously,the method can be run with high differential pressure or multipasspressure, and no bypassing of tubeside fluid occurs around the passpartition plate.

According to another embodiment of the invention, a method is providedfor retrofitting an existing multipass tubular heat exchanger. Thismethod is particularly appropriate to repair heat exchangers in whichthe pass partition plate has already been damaged by high differentialpressure use, or to make a conventional heat exchanger suitable for highdifferential pressure use. According to this method, the existingtubesheet and existing pass partition plate are removed from the heatexchanger and replaced with a curved pass partition plate as describedherein and corresponding tubesheet. According to one embodiment of theinvention, the curved pass partition plate and corresponding tubesheetare provided as a matched set. According to another embodiment of theinvention, a semi-enclosed channel cover is conveniently provided inwhich the nonplanar pass partition plate is fixed within the channel andthe free edge of the pass partition plate is curved.

1. A multipass tubular heat exchanger comprising: a plurality of tubesconfigured to contain a tubeside fluid, the plurality of tubes having atleast one set of terminal ends; a planar tubesheet comprising aplurality of apertures for receiving the ends of the tubes; a channelhaving a tubeside fluid inlet and a tubeside fluid outlet, the channelpositioned adjacent the tubesheet such that the channel and tubesheettogether define an internal space in fluid communication with the tubes;and a nonplanar pass partition plate positioned in the internal spaceconfigured to divide the internal space into an inlet space in fluidcommunication with the tubeside fluid inlet and an outlet space in fluidcommunication with the tubeside fluid outlet, thereby to prevent directfluid communication between the tubeside fluid inlet and the tubesidefluid outlet and to direct fluid flow through the tubes; wherein thepass partition plate has an edge which is fixed to the tubesheet, theedge having a radius of curvature about an axis extending generallyperpendicular to the tubesheet.
 2. The multipass tubular heat exchangerof claim 1 wherein the planar tubesheet further comprises a groove forreceiving the pass partition plate, the groove having a length, athickness, two endpoints and a midpoint; and wherein the pass partitionplate further comprises a mating edge which fits into the groove of thetubesheet; wherein the groove of the tubesheet and the mating edge ofthe pass partition plate each have a radius of curvature about an axisextending generally perpendicular to the tubesheet such that themidpoint of the groove is a greater distance from a straight linepassing through the endpoints of the groove than the thickness of thegroove.
 3. The multipass tubular heat exchanger of claim 1 furthercomprising: a shell enclosing the plurality of tubes for containing ashell fluid, the shell having a first end and a second end and having ashell fluid inlet and a shell fluid outlet; wherein the tubesheet issecured to the first end of the shell.
 4. The multipass tubular heatexchanger of claim 1 further comprising a gasket between the channel andthe tubesheet.
 5. The multipass tubular heat exchanger of claim 4wherein the gasket includes a rib portion adjacent and between the passpartition plate and the groove of the tubesheet.
 6. The multipasstubular heat exchanger of claim 1 wherein the midpoint of the groove isa greater distance from a straight line passing through the endpoints ofthe groove than the distance between the endpoints of the groove dividedby
 100. 7. The multipass tubular heat exchanger of claim 1 wherein theheat exchanger is an air cooled heat exchanger in which heat isexchanged between the tubeside fluid within the plurality of tubes andair moving over the plurality of tubes.
 8. The multipass tubular heatexchanger of claim 1 wherein the plurality of tubes comprise straighttubes having openings on each end received by apertures in a tubesheeton each end in fluid communication with a channel on each end adjacentthe tubesheet.
 9. The multipass tubular exchanger of claim 1 wherein theplurality of tubes comprise U-shaped tubes.
 10. The multipass tubularheat exchanger of claim 1 comprising multiple pass partition plates. 11.The multipass tubular heat exchanger of claim 1 comprising multiplegrooves.
 12. The multipass tubular heat exchanger of claim 1 wherein theradius of curvature is in the direction of the tubeside fluid inlet. 13.The multipass tubular heat exchanger of claim 1 wherein the radius ofcurvature is in the direction of the tubeside fluid outlet.
 14. Amatching pass partition plate and tubesheet for use in a multipasstubular heat exchanger comprising: a planar tubesheet comprisingapertures for receiving ends of heat exchanger tubes and a groove forreceiving a pass partition plate, the groove having a length, athickness, two endpoints and a midpoint; a nonplanar pass partitionplate having a mating edge which fits into the groove of the tubesheet;wherein the groove of the tubesheet and the mating edge of the passpartition plate each have a radius of curvature about an axis extendinggenerally perpendicular to the tubesheet such that the midpoint of thegroove is a greater distance from a straight line passing through theendpoints of the groove than the thickness of the groove.
 15. A channelcover for use in a multipass tubular heat exchanger comprising: asemi-enclosed channel having a planar open end and configured to definean internal space when the open end is positioned adjacent a planartubesheet; and a nonplanar pass partition plate having peripheral edgesfixed within the channel and a free edge in the plane of the open endwherein the free edge has a radius of curvature about an axis extendinggenerally perpendicular to the plane of the open end.
 16. A method ofretrofitting a multipass tubular heat exchanger having an existingtubesheet and an existing pass partition plate, comprising: removing theexisting tubesheet and the existing pass partition plate; installing aplanar tubesheet comprising a plurality of apertures for receiving endsof heat exchanger tubes and a groove for receiving a pass partitionplate; and a nonplanar pass partition plate having a mating edge whichfits into the groove of the tubesheet; wherein the groove of thetubesheet and the mating edge of the pass partition plate each have aradius of curvature about an axis extending generally perpendicular tothe tubesheet.
 17. A method of exchanging heat between a tubeside fluidflowing through a plurality of tubes in a multipass tubular heatexchanger and a fluid surrounding the plurality of tubes, comprising:introducing a tubeside fluid into an internal space defined by a channeland a planar tubesheet having a plurality of apertures, the internalspace being in fluid communication with a plurality of tubes having aplurality of a tubeside fluid inlet ends aligned with a first portion ofthe plurality of apertures of the tubesheet and a plurality of tubesidefluid outlet ends aligned with a second portion of the plurality ofapertures of the tubesheet; and flowing the tubeside fluid into theplurality of tubes through the first portion of the plurality ofapertures and through the plurality of tubes between the tubeside fluidinlet ends and the tubeside fluid outlet ends such that the tubesidefluid exits through the second portion of the plurality of aperturesinto the internal space; wherein the tubeside fluid exiting the tubes isseparated from the tubeside fluid entering the tubes by a nonplanar passpartition plate dividing the internal space having an edge in contactwith the tubesheet which has a radius of curvature about an axisperpendicular to the tubesheet; wherein no bypassing of tubeside fluidoccurs around the pass partition plate.